A number of companies provide Internet based betting services. The majority of these are simply an extension of conventional betting services, offering fixed odds betting in which customers only have access to one side of the market, i.e. they can only efficiently back, or “buy”, a particular outcome to occur at odds set by the bookmaker. However, it is often far easier to decide what is not going to occur rather than trying to decide what will occur. In this situation, though, customers are not able to place a bet to support their view. While it is true that they can try to simulate laying, i.e. “selling” the outcome by backing all other possible outcomes, this is highly unlikely to be profitable due to the overround charged by the bookmaker. The overround is the extent to which the bookmaker's total book exceeds 100% and represents the bookmaker's primary source of profit. In the UK, a typical overround is 10-15%.